1. Technical Field
The present invention relates to a display medium, a manufacturing method of the same, and also an apparatus for manufacturing the display medium.
2. Related Art
Attention has recently been focused on a display medium using a cholesteric liquid crystal due to it having a memorization ability whereby a display can be maintained even when the power has been turned off, and because it is capable of obtaining a bright display because no polarization plate is used, and because it is capable of performing color display without using a color filter (see Japanese Patent Application Laid-Open (JP-A) No. 5-80303).
The cholesteric liquid crystal is composed of rod-like molecules oriented in a helical manner, and has the property of performing interferential reflection of light coinciding with a helical pitch of the liquid crystal (this reflection is also referred to as “selective reflection”). Thus, due to the helical pitch being set to have a magnitude corresponding to each of the wavelengths of red light, green light and blue light, the cholesteric liquid crystal can display colors brightly without using a color filter.
On the other hand, a binder dispersion type display medium is known in which display material is dispersed and held in a binder, for example, a display medium in which microcapsules holding the display material are dispersed in a binder material such as a resin. Examples of the display medium include: an electrophoretic display element in which insulating oil containing charged color particles is formed into microcapsules; a magnetophoresis display element in which insulating oil containing magnetic particles is enclosed in microcapsules; a liquid crystal display medium in which liquid crystal material is enclosed in microcapsules; and the like.
Further, a display medium is also known in which a display material is processed into a liquid and dispersed in a solution of a binder material in which the display material is insoluble, and then applied by coating and dried. For example, a liquid crystal display element having a display element manufactured by applying and drying a liquid crystal material dispersed in an aqueous solution of a water-soluble resin. Moreover, a display element in which a binder material and a display material are uniformly dissolved using solubilizing means such as a solvent or heating, and then phase-separated from each other by adding external stimulation such as heat or light is also known. Examples thereof include a polymer dispersion type liquid crystal display element prepared by phase separation of a resin and a liquid crystal material from a co-solvent solution by solvent drying, and a polymer dispersion type liquid crystal display element prepared by using photo-polymerization phase separation from a mixed solution of a photo-polymerization monomer and a liquid crystal material.
In the aforementioned binder dispersion type display medium, a display material is dispersed and enclosed in a binder solution, and therefore, the processes of forming containers and enclosing the display material in capsules are not required. Further, the thickness of the material is maintained due to the strength of the binder, and therefore, it is not necessary to provide a spacer. The binder serves as a wall, and therefore, a process of forming a flow prevention wall is not required. Hence, the structure may be simplified and the number of manufacturing processes reduced, which reduces costs.
In the binder dispersion type display medium described above, generally, a display layer is formed by coating a substrate with a binder solution in which a display material is dispersed. For the purpose of protecting the coated surface or providing a functional layer thereon, another substrate may be bonded on the display layer. In particular, when the display material is a voltage response type material and display of a desired pattern or an arbitrary pattern is desired, a display layer is interposed between a pair of substrates having, transparent conductive films such as ITO (Indium Tin Oxide) as electrodes formed therein, so as to apply a voltage to the display layer.
In this case, first the display layer is applied and formed on one of the electrode-attached substrates, and subsequently, the other electrode-attached substrate having the functional layer or the like formed thereon is bonded to the display layer, and thus the display medium is manufactured.
A liquid crystal display medium in which the liquid crystal material is enclosed in microcapsules is known, the display medium being formed such that a cholesteric liquid crystal contains a polymer or solid matter such as a microcapsule shell, and a semi-solid display layer is formed overall (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2005-316243).
In manufacturing the aforementioned display medium, it is effective to use a method in which a microcapsule dispersion liquid is applied to one of the substrates, and thereafter, the substrate is bonded to the other substrate in air, which facilitates production of a large-size liquid crystal element and highly efficient production of a large-area liquid crystal element.
The development of the aforementioned display medium for use as electronic paper (E-paper) has also been proceeding. For applications of the display medium, a display medium that allows high image quality is desired. Particularly, in order to display small-size characters, improvements regarding the resolution and graininess of images are desired.